Panum's phenomenon and the confluence of signals from the two eyes in stereoscopy

The signals from the two eyes must be routed to allow either eye to have access to the processing mechanisms for position, shape, colour, etc.; at the same time, information as to the eye of origin must be retained for the purposes of stereoscopy. The study of this confluence of signals from the two eyes was approached psychophysically by studying induced position and depth changes of adjacent binocular and monocular stimuli in the human fovea. It was demonstrated that a monocular visual stimulus located near a binocular one acquires a depth signal, according to a scheme originally proposed by Panum. The effect is unspecific as regards feature shape and brightness, and falls off with a length constant of about 15 minutes of arc in the fovea. A monocular stimulus also affects the apparent depth of its binocular neighbour in a centre-surround manner; disparity pooling changes to disparity repulsion when features are separated by distances of about 3 minutes of arc in the fovea. The findings led to the development of a scheme of uniocular connectivity to a matrix of depth units. Excitation patterns here would depend on the state of the input lines, the intrinsic neuronal interaction properties, and contextural configuring influences from other parts of the nervous system. Experiments showing the spatial extent of pooling and repulsive interaction within the disparity domain help to characterize the stimulus processing in this neural ensemble.